In a typical vehicle to which this invention pertains, a pair of wheels are driven through a differential which divides and applies engine torque to the wheels attached to the differential by way of axles. In conventional drive trains such as those found on highway and off-highway vehicles, the differentials operate to transfer torque to the wheel having the lowest traction. Limited slip and locking differentials are used on some vehicles to provide a means for transferring engine torque to the wheel with the most traction. Limited slip and locking differentials, however, can be very expensive and, in the case of limited slip differentials, may not be sufficiently effective to transfer torque to a wheel sitting on an extremely low traction surface, such as ice.
More recently, traction control systems which utilize the braking system to control wheel slip have been introduced. In many, if not most of these systems, when wheel slip is detected, the brakes of the faster rotating wheel are applied to reduce its speed to that of the non-slipping wheel. Many of these systems are complex and add significant cost to the vehicle.